A thin film transistor substrate and a fabricating method thereof for simplifying a process are disclosed. In a liquid crystal display device according to the present invention, a gate line is provided on a substrate. A data line crosses the gate line with having a gate insulating film therebetween to define a pixel area. A thin film transistor includes a gate electrode connected to the gate line, a source electrode connected to the data line, a drain electrode opposed to the source electrode and a semiconductor layer for defining a channel between the source electrode and the drain electrode. A pixel electrode is connected to the drain electrode and is provided at said pixel area. Herein, said data line, said source electrode and said drain electrode have a double-layer structure in which a source/drain metal pattern and a transparent conductive pattern are built. Said pixel electrode is formed by an extension of the transparent conductive pattern of the drain electrode. A protective film makes a border with the transparent conductive pattern and provided at the remaining area thereof.